This project consists of a three-year program of research into the functioning of the voice source in speech and singing. The research can be divided into five areas, summarized as follows: (1) The effect of transglottal and intraglottal pressure on vocal fold action will be measured by inducing brief perturbations in subglottal and supraglottal pressure. (2) The pattern of vocal fold movements during their closing phase will be investigated, using simultaneous recordings of inverse-filtered pharyngeal pressure, inverse-filtered air flow and an electro-glottograph, and the aerodynamic consequences examined by mathematical analysis. (3) Two techniques will be investigated for adapting the hot-wire principle for flow measurement to the low velocity, fluctuating and reversing flow encountered in voiced speech production. A prototype anemometer employing the most promising technique will be used for the corroboration of wire-screen anemometer measurements of volume velocity and to measure particle velocity distribution in a mechanical vocal tract model. (4) Previous results will be expanded in relating source-tract acoustic interaction to vocal efficiency in soprano singing and in determining the interactive effects having the most influence on voice quality in intermediate ranges of FO in professional singing. (5) Our previous investigation of the aerodynamics of vibrato in singing will be continued and expanded to other types of vocal tremor.